Driving unit for loud-speakers



July 5, 1932. p U H 1,866,361

DRIVING UNIT FOR LOUD SPEAKERS Filed Aug. 14, 1930 a -llll 'ii iiliiiiii'ii;

Inventor".

Hans P KuehnL 9 Hi s Aug)? 'r eg,

" the gap to permit the free vibration therein Patented July 5, 1932 jrs ATENT HANS I. KUEHNI, 0F SGHENEGTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW"YORK DRIITING "UNIT FORLOUD-SPEAKERS Application filed August 14, 1930. Serial No. 475,233.

My invention relates to speech current devices for converting electricoscillation into sound waves or vice versa, particularly to loud speakerdevices of the moving coil type, and has for its principal object theprovision of an improved driving unit for such devices.

In the use of loud speakers in which 2. diaphragm is driven by a coilmoving in an air gap formed by a magnet structure it is clesirable thatthe gap be short in order to permit the production of a strong magneticfield in the gap by the use of only a comparatively small magnetstructure, or in certain cases by the use of a permanent magnet ormagnets. But di'fiiculties have been encountered heretofore in theattempt to provide an efficient loud speaker comprising a moving coiland at the same time having a short air gap, due to the comparativelywide space required at of the moving coil system commonly used,comprising a coil or coils of many turns connected directly to a sourceof current varying in accordance with sound waves and mounted on a stiffsupporting member, usually a cylinder rigidly fastened to a conediaphragm.

In accordance with my invention I have provided an efficient loudspeaker which is of the moving coil type but in which the air I gapformed by the magnet structure is Very short. To accomplish this resultthe speech current source is not connected to a moving coil but to astationary coal or coils mounted on a core, and the moving coil isreplaced by a flat, single turn, short-circuited conducting member inwhich the currents actuating the diaphragm are induced by transformeraction. It is a feature of my invention that by reason of the short airgap characterizing the driving unit for the loud speaker a strongmagnetic field may be produced, sufficient for the satisfactoryoperation of a cone type loud speaker in many uses, by permanentmagnets, thereby avoiding the necessity of providing electromagnets forthis purpose.

It is a further feature of my invention that the transformerincorporated in this driving unit may replace the transformer usuallyconnected between the power tube of a radio receiver and the loudspeaker.

My invention will be better understood from the followingdescriptionwhen consideredin connection with the accompanying drawingand its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a side elevation of a speech currentdevice embodying my invention; Fig. 2 is an enlarged perspective view ofa part of this device; and I Fig. 3 is a sectional view on line 11 ofFig. 1.

In the embodiment of the invention shown in the drawing the speechcurrent device is a loud speaker comprising a cone diaphragm 10 actuatedby a driving unit 11 of the moving coil type in' which a magnetic fieldis produced by a magnetic unit 12 and the moving coil forms part of aspeech current transformer 13. In the magnetic unit 12 a frame memberv14 is provided on which are mounted two oppositely disposed, preferablypermanent magnets 15, 16 so arranged that poles of opposite polarityare'dispos edadjacent each other to form two air gaps 17 18. The

transformer 18 comprises a core member 19 having a' leg 20 and twoprimary coils-2l, 22 at the ends thereof, mounted on the magnetic unit12 as by studs 23 and so arranged that the magnets 15,16 surround thecore.

The core leg 20 is disposed centrally in the I space enclosed by themagnets and at right angles to the plane of the air gaps 17 18. Thesecondary of transformer, 13 is a shortcircuited winding member 24%constituting the moving coil of the loud speaker driving unit 11.Winding member 2 1 is a thin, flat, rectangular plate of suitablecurrent conducting material such as copper or aluminum arranged tosurround the core leg 20.- The central portions of the two oppositesides 25, 26 of the plate are disposed closely adjacent to the corelegto reduce the leakage reactance and between adjoining ends of the twoprimary coils 21, 22, and the side portions 27 and 28 are disposedrespectively in the air gaps 17 and 18. The side portions 27 and 28 maybe as long as orlonger than the side portions 25,26 in order that arelatively large part of member 24; maybe disposed in the air gaps. Theplate 24: is maintained in proper position by suspension means whichcomprise strings 29 connected to the corners of the plate and which maybe made adjustable by attaching the strings to adjusting screws 30. Thecone 10 is connected to the plate 2d at one side thereof, as by adriving rod 31 fastened to a lug 32 formed at the center of plate side27.

In the operation of the above described loud speaker device embodying myinvention, speech currents from any suitable source (not shown), such asa. radio receiver, are causedto flow in the primary coils 21, 22 oftransformer 13. A varying secondary current corresponding to the speechcurrent in these coils is thereby induced in the shortcircuitedsecondary winding constituted by the'plate 24 surrounding the coreleg ofthe transformer. This varying secondary current flows in the portions27, 28 of plate 24 which are suspended in the air gaps 17, 18 and theentire plate, of which these portions form a part, vibrates in the planeof the plate and in the direction of the cone driving rod 31, under theinfluence of the magnetic field produced in the air gaps by the magnets15, 16 of the magnetic unit 12, thereby vibrating the rod and thediaphragm attached thereto.

It will be seen that since the flat portions 27, 28 of the single turnsecondary winding 24 which constitutes the speech current conductorsmoving in the magnetic field in air gaps 17, 18 are relatively thin, andsince the motion of these conductors is in the plane of the flat surfacethereof, therefore, the gap between adjacent poles of the magnet unitextending in opposite directions from said winding substantially atright angles to the plane thereof.

2. A speech current device including a vibratable member, ashort-circuited flat rectangular winding connected thereto, a speechcurrent transformer comprising a core member and said winding, a magnetstructure arranged to surround said core member and having twooppositely disposed magnets forming a pair of air gaps, said windingbeing arranged to. surround said core member and having oppositelydisposed portions is of such length only as to provide for the insertionof a thin plate between the poles and for the small clearance spacerequired for ed ewise movement of the plate in the gap. t will be seenfurther that by reason of the fact that it is thus possible to maintainthe air gaps 17, 18 extremely short, a high field intensity may beprovided by a magnet unit 12 comprising permanent magnets.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A speech current device including a vibratable member, ashort-circuited flat winding connected thereto, a speech currenttransformercomprising a core member and said winding, a magnet structurearranged to surround said core member and having two oppositely disposedmagnets forming a pair of air gaps, said winding being arranged tosurround said core member andhaving oppositely disposed portions eacharranged to move in the same direction in a different one of said airgaps, and means to suspend said fiat winding comprising pairs of flex-

